Abstract
In plants, PCNA (proliferating cell nuclear antigen) gene is expressed periodically during G1 to S phase, and is thought to be regulated by pRB pathway. To elucidate how tobacco PCNA gene expression is regulated, we have constructed experimental system using the transient assays in tobacco BY-2 cells, and showed that transcription of PCNA is activated by NtE2F/NtDP complex. This transcriptional activation was repressed when co-expressed with NtRBR1, whereas this repressive activity of NtRBR1 was canceled by further co-expressed with cyclin D but not with cyclin A or cyclin B.
Additionally, we have performed the experiment using synchronized culture of BY-2 cells transformed with tobacco PCNA promoter fused to a luciferase gene. Mutation of two E2F binding sites caused significantly reduction of promoter activity, suggesting that the two E2F binding sites synergistically contribute to up-regulate the expression of PCNA promoter at G1/S phase.
